Isolator for alternator pulley

ABSTRACT

A decoupler for an alternator pulley in a serpentine drive system has a resilient, helical spring member that couples the alternator pulley with a hub structure through a spring retaining member. A bushing is disposed between the spring retaining member and the hub structure to facilitate sliding engagement therebetween. An annular sleeve member is disposed between the spring member and the alternator pulley to facilitate sliding engagement therebetween. The spring member is connected at one end thereof to the hub structure and connected at an opposite end thereof to the spring retaining member. The resilient spring member transmits the driven rotational movements of the alternator pulley by the serpentine belt to the hub structure such that the alternator shaft is rotated in the same direction as the alternator pulley while being capable of instantaneous relative resilient movements in opposite directions with respect to the alternator pulley during the driven rotational movement.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a decoupler and moreparticularly to an alternator decoupler for a serpentine accessory drivesystems for automotive vehicles.

[0003] 2. Description of Related Art

[0004] Serpentine accessory drive systems typically includes a drivingpulley on the output shaft of the internal combustion engine of thevehicle, a series of driven pulleys for the accessories and a poly-Vbelt trained about the driving and driven pulleys. An advantage of theserpentine drive is that, by providing an automatic belt tensioner onthe belt, the accessories can be fixedly mounted.

[0005] Particularly where the engine is of the four-cylinder type, thedriving pulley establishes a highly dynamic loading on the belt. Thishigh dynamic loading is due to the variable torque outputcharacteristics of such engines. Under this circumstance, the tensionercannot accommodate all of the variable torque characteristics. Theresult is sometimes noise and decreased belt life due to instantaneousbelt slippage. It has been proposed to provide an engine crank shaftdecoupler in order to deal with the high dynamic belt loading. Thissolution, while effective, is costly since the decoupler must have acapacity generally equal to the system capacity.

[0006] It has also been proposed in U.S. Pat. No. 5,139,463 of commonownership with the present invention and which is hereby incorporated byreference in its entirety for its teachings as they relate to thepresent invention, to provide an alternator assembly wherein a coilspring is provided between an alternator pulley and alternator hubstructure for transmitting the driven rotational movements of thealternator pulley by the serpentine belt to the hub structure such thatthe alternator armature assembly is rotated in the same direction as thealternator pulley while being capable of instantaneous relativeresilient rotational movements in opposite directions with respect tothe alternator pulley during the driven rotational movement thereof.This has proven to be a cost effective manner of accommodating highdynamic belt loading to reduce noise and preserve belt life.Nevertheless, it can be appreciated that the coil spring employed issubject to significant stresses over the life of the alternator. It istherefore an object of the present invention to reduce stress on thespring and thereby increase the life thereof.

SUMMARY OF THE INVENTION

[0007] The above and related objects of this invention are realized byproviding a serpentine belt drive system for an automotive vehiclecomprising a drive assembly including an internal combustion enginehaving an output shaft with a driving pulley thereon rotatable about adriving pulley axis, a sequence of driven assemblies each having adriven pulley rotatable about an axis parallel with said driving pulleyaxis and a serpentine belt mounted in cooperating relation with saiddriving pulley and with said driven pulleys in a sequence whichcorresponds with the sequence of said driven assemblies when related tothe direction of movement of the belt to cause said driven pulleys torotate in response to the rotation of said driving pulley. The drivesystem further includes a sequence of driven assemblies including analternator assembly including a housing and an armature assembly mountedin the housing for rotation about an armature axis. A hub structure isfixedly carried by the armature assembly outwardly of the housing forrotation therewith about the armature axis. An alternator pulley ismounted on the hub structure for rotational movement about the armatureaxis. A coil spring resiliently couples the alternator pulley with thehub structure, the coil spring transmitting the driven rotationalmovements of the alternator pulley by the serpentine belt to the hubstructure such that the armature assembly is rotated in the samedirection as the alternator pulley while being capable of instantaneousrelative rotational movements in opposite direction with respect to thealternator pulley during the driven rotational movements thereof. Aninner spring engaging structure is rotationally fixed with respect tothe pulley and engages volutes of the coil spring as a result of radialcontraction of the coil spring.

[0008] Other aspects of the invention are achieved as follows:

[0009] A serpentine belt drive system for an automotive vehiclecomprising a drive assembly including an internal combustion enginehaving an output shaft with a driving pulley thereon rotatable about adriving pulley axis, a sequence of driven assemblies each having adriven pulley rotatable about an axis parallel with the driving pulleyaxis and a serpentine belt mounted in cooperating relation with thedriving pulley and with the driven pulleys in a sequence whichcorresponds with the sequence of the driven assemblies when related tothe direction of movement of the belt to cause the driven pulleys torotate in response to the rotation of the driving pulley, the sequenceof driven assemblies including an alternator assembly including ahousing and an armature assembly mounted in the housing for rotationabout an armature axis; a hub structure fixedly carried by the armatureassembly outwardly of the housing for rotation therewith about thearmature axis, an alternator pulley is mounted on the hub structure forrotational movement with respect to the hub structure about the armatureaxis; an outer spring engaging structure disposed between the alternatorpulley and the coil spring, the outer spring engaging structure engagingvolutes of the coil spring as a result of radial expansion of the coilspring; and a coil spring resiliently coupling the alternator pulleywith the hub structure, the coil spring transmitting the drivenrotational movements of the alternator pulley by the serpentine belt tothe hub structures such that the armature assembly is rotated in thesame direction as the alternator pulley while being capable ofinstantaneous relative rotational movements in opposite directions withrespect to the alternator pulley during the driven rotational movementthereof, an outer spring engaging structure disposed between thealternator pulley and the coil spring, the outer spring engagingstructure engaging volutes of the coil spring as a result of radialexpansion of the coil spring.

[0010] A serpentine belt drive system for an automotive vehiclecomprising a drive assembly including an internal combustion enginehaving an output shaft with a driving pulley thereon rotatable about adriving pulley axis, a sequence of driven assemblies each having adriven pulley rotatable about an axis parallel with the driving pulleyaxis and a serpentine belt mounted in cooperating relation with thedriving pulley and with the driven pulleys in a sequence whichcorresponds with the sequence of the driven assemblies when related tothe direction of movement of the belt to cause the driven pulleys torotate in response to the rotation of the driving pulley, the sequenceof driven assemblies including an alternator assembly including ahousing and an armature assembly mounted in the housing for rotationabout an armature axis; a hub structure fixedly carried by the armatureassembly outwardly of the housing for rotation therewith about thearmature axis, an alternator pulley mounted on the hub structure forrotational movement about the armature axis; a coil spring resilientlycoupling the alternator pulley with the hub structure, the coil springtransmitting the driven rotational movements of the alternator pulley bythe serpentine belt to the hub structure such that the armature assemblyis rotated in the same direction as the alternator pulley while beingcapable of instantaneous relative rotational movements in oppositedirections with respect to the alternator pulley during the drivenrotational movement thereof, the alternator pulley being mounted foraxial movement relative to the hub, the coil spring axially expandingduring radial contraction thereof and thereby applying an increasingaxial damping force on the pulley so as to dampen rotational movement ofthe pulley relative to the hub structure.

[0011] A decoupler has a hub structure capable of being mounted on ashaft; a pulley mounted on the hub structure and capable of relativerotational movement with respect to the hub structure; a coil springresiliently coupling the pulley with the hub structure, the coil springcapable of transmitting driven rotational movements of the pulley to thehub structure; an inner spring engaging structure rotationally fixedwith respect to the pulley and engaging volutes of the coil spring as aresult of radial contraction of the coil spring.

[0012] A decoupler has a hub structure capable of being mounted on ashaft; a pulley mounted on the hub structure and capable of relativerotational movement with respect to the hub structure; a coil springresiliently coupling the pulley with the hub structure, the coil springcapable of transmitting driven rotational movements of the pulley to thehub structure; an outer spring engaging structure disposed between thealternator pulley and the coil spring, the outer spring engagingstructure engaging volutes of the coil spring as a result of radialexpansion of the coil spring.

[0013] A decoupler has a hub structure capable of being mounted on ashaft; a pulley mounted on the hub structure and capable of relativerotational movement with respect to the hub structure; a coil springresiliently coupling the pulley with the hub structure, the coil springcapable of transmitting driven rotational movements of the pulley to thehub structure; the pulley being mounted for axial movement relative tothe hub structure; and the coil spring axially expanding during radialcontraction thereof and thereby applying an increasing axial dampingforce on the pulley so as to dampen rotational movement of the pulleyrelative to the hub structure. dr

DESCRIPTION OF THE DRAWINGS

[0014] The present invention is further described in the detaileddescription which follows, by reference to the noted drawings by way ofnon-limiting exemplary embodiments, in which like reference numeralsrepresent similar parts throughout the several views of the drawings,and wherein:

[0015]FIG. 1 is a front elevational view of an automobile internalcombustion engine having a serpentine drive system embodying theprinciples of the present invention connected therewith;

[0016]FIG. 2 is an enlarged fragmentary sectional view of the firstembodiment of the isolator device taken along the line 2--2 of FIG. 1;

[0017]FIG. 3 is an enlarged fragmentary sectional view of an alternateembodiment of a mounting arrangement of the alternator pulley to the hubstructure;

[0018]FIG. 4 is an enlarged fragmentary sectional view showing analternate embodiment having a coil spring with varying diameter coils;and

[0019]FIG. 5 is an enlarged fragmentary sectional view showing analternate embodiment of the isolator device of the present invention.

DETAILED DESCRIPTION

[0020] Referring now more particularly to the drawings, there is shownin FIG. 1 an automotive internal combustion engine, generally indicatedat 10, which includes a schematically indicated engine frame 12 and anoutput shaft 14. Fixed to the output shaft 14 is a driving pulley 16forming part of a serpentine drive system, generally indicated at 18.The drive system 18 includes an endless belt 20. The belt 20 is of thethin flexible type, as, for example, a poly-V belt. The belt 20 istrained about the driving pulley 16 and a sequence of driven pulleyassemblies 22, 24, 26, 28, and 30, each of which is fixed to arespective shaft 32, 34, 36, 38, and 40. Except for the pulley assembly22, which is a simple idler pulley, the shafts are connected to operatevarious engine or vehicle accessories. For example, shaft 34 drives anengine water pump, shaft 36 an electrical alternator, shaft 38 anelectromagnetic clutch of a compressor for an air-conditioning systemfor the automobile, and shaft 40 an oil pump of the power steeringsystem.

[0021] It will be understood that the internal combustion engine 10 maybe of any known construction. In accordance with conventional practice,the operation of the engine is such as to impart vibratory forces to theengine frame 12. All of the accessories are mounted on the engine frame12 so that the shafts are rotated about parallel axes which are fixedwith respect to the engine frame 12 and parallel with the output shaft14 thereof. The belt 20 is tensioned by a belt tensioner, generallyindicated at 42 which may be of any construction. However, a preferredembodiment is the tensioner disclosed in commonly assigned U.S. Pat. No.4,473,362, the disclosure of which is hereby incorporated by referenceinto the present specification.

[0022] As shown, the belt tensioner 42 includes an idler pulley 44 whichis disposed in rolling engagement with the flat back surface of the belt20, the tensioner pulley being spring biased to maintain a generallyconstant tension in the belt 20.

[0023] As best shown in FIG. 2, the present invention is moreparticularly concerned with the functional connection between thepulley, generally indicated at 26, and the shaft 36 of the alternator.The alternator includes a housing 46 within which the armature assembly,generally indicated at 48, is journalled, as by bearings 50. As shown,alternator shaft 36 forms a part of the armature assembly 48 andincludes an end portion extending outwardly of the alternator housing46.

[0024] The pulley 26 forms part of a coupling assembly 29, which ismounted on the shaft 36, for coupling the belt 20 to the shaft 36.Coupling assembly 29 also includes, among other elements, the hubstructure, generally indicated at 52, which is fixed to the outwardlyextending end of the alternator shaft 36. As shown, the hub structure 52includes an inner sleeve portion 54 which, in the illustratedembodiment, extends over the end of the alternator shaft 36 end portion.In other embodiments, depending on the alternator and pulley geometry,the inner sleeve portion 54 may not extend over the end of thealternator shaft 36 end portion. As shown, the extremity of the shaft 36is threaded as indicated at 56 and the sleeve 54 is formed with a seriesof interior threads 58 which are disposed in meshing relation with thethreads on the end of the shaft 36. The inner surface 53 of the hubstructure 52 at the outer axial end 60 thereof may be formed of a innertoothed sprocket for receiving a correspondingly configured tool torotate the hub 52 onto the shaft for threadedly securing the hubstructure 52 on the shaft 36. Alternatively, the annular end surface 60may be formed to provide a hexagonal socket for receiving a tool forsecuring the sleeve 54 over the shaft 36 by relative rotation betweenthe sleeve 54 and shaft 36, as known in the art. It can be seen that asthe sleeve portion 54 is threaded on the end of the shaft 36, theaxially inner end surface thereof is squeezed one side of the inner raceof the ball bearing 50 against a flange 64 on the shaft 36 and the otherside of the inner race of the ball bearing 50 with the inner race of aball bearing 50 mounted on the shaft 36 in abutting relation with theball bearing 50.

[0025] As best shown in FIG. 2, the alternator pulley 26 includes anannular pulley member 68 having an exterior poly-V surface 70 forrollingly engaging the operative poly-V side of the serpentine belt 20.One end of the annular pulley member 68 has axial flange 72, whichincludes a radially inwardly extending portion 71 and then an axiallyextending portion 73 as shown. Flange 72 may also include a radiallyoutwardly extending end portion 75 as shown. The inner surface 69 of theflange 72 is disposed in engagement with an L-shaped, annular bushing orbearing 78. The annular bushing 78 is preferably an integral structurehaving an axial extending portion 79 having a radially outer surfacedisposed in engagement with an portion 73 of flange 72, and a radiallyinner surface disposed in engagement with a contact surface 80 at theend of the hub structure 52. The annular bushing 78 preferably alsoincludes a radial extending portion 128 having an axially outer surfacedisposed in engagement with radially inwardly extending portion 71 ofthe flange portion 72, and an axially inner surface thereof disposed inengagement with a radially outwardly extending portion 57 of hubstructure 52 as described below. Although the annular bushing 78 isshown as an integral structure, the annular bushing may also includeseparate structures: an axial portion, corresponding to axial portion79, and a radial portion, corresponding to radial portion 128. Theannular bushing 78 supports relative motion between the pulley 26 andthe shaft 36. The annular bushing 78 may be made of a material having alow coefficient of friction to facilitate sliding action between thepulley 26 and the hub 52. For example, the annular bushing 78 may be apolymeric material. The material of the annular bushing 78 may also ametal, such as brass, or a lead-alloy. A lubricant may also be used atthe interface between the annular bushing 78 and pulley 26 to facilitatesliding contact therebetween. The bushing 78 may be fixed relative toone of the hub 52 or pulley 26, or may be movable (slidable) withrespect to both. Alternatively, as shown in FIG. 3, rather than usingannular bushing 78, a ball bearing 77 may be disposed between the flangeportion 72 and the contact surface 80 of the hub structure 52 to supportthe relative motion between the pulley 26 and the hub 52. In such aconfiguration, a thrust washer 127 is utilized in place of the radialportion 128 of the annular bushing 78 between the radially inwardlyextending portion 71 of the pulley and the protruding portion 57 of thehub 52.

[0026] The hub structure 52 includes the forementioned radiallyprotruding portion 57 (hereinafter referred to as the radial portion 57)and an axially inwardly extending portion 59 integrally formed thereon.In the illustrated embodiment, the portion 59 extends axially from theend of the radial portion 57 toward the alternator assembly 46.Alternatively, the orientation of the portion 59 and radial portion 57may be reversed to permit the poly-V surface 70 of the annular pulleymember 68 to be located closer to or further away from the alternatorhousing. A clearance gap G4 is maintained between the inner surface 84of the pulley 26 and the outer surface 63 of the axial portion 59 of thehub structure 52 so that the pulley rotates freely thereabout. It can beseen that the mounting of the pulley 26 with respect to the hubstructure 52 is such as to define an annular space 86 therebetween,generally defined by the pulley 26, the sleeve portion 54 and radial 57portion of the hub structure. Disposed within this annular space 86,between an inner surface 84 of the pulley 26 and the outer surface 88 ofthe hub structure 52, is a spring retaining member made of low carbonsteel, generally indicated at 92. The spring retaining member 92(hereinafter referred to as the spring retainer 92) is formed of anannular cylindrical inner portion 96 and an annular cylindrical outerportion 100 connected by a radial wall portion 104. An exteriorcylindrical surface 108 of the outer portion 100 frictionally engagesthe cylindrical interior surface portion 74 of the pulley 27, via apress-fit, for example, to form a rigid connection therebetween. Asecond annular radial bushing 112 is disposed between the inner surface116 of the inner portion 96 of spring retainer 92 and the outer surface88 of the sleeve portion 54 of the hub structure 52. Bushing 112includes a flange 113 disposed at one end. Specifically, bushing 112 ispress-fit to retainer 92 and is thus fixed to spring retainer 92. Thesecond radial bushing 112 further supports the relative motion betweenthe pulley 26 (via spring retainer 92) and the hub structure 52. Theradial bushing 112 may be made of a material having a low coefficient offriction to facilitate sliding action between the spring retainer 92 andthe hub 52. For example, the radial bushing 112 is preferably made froma steel material with teflon bonded on an inner surface thereof thatengages sleeve 54. The material of the radial bushing 112 may also ametal, such as brass, or a lead-alloy. A lubricant may also be used atthe interface between the second radial bushing 112 and inner portion 96of the sleeve retainer 92 to facilitate sliding contact therebetween.The flange 113 is generally made of the same material as the bushing112, and a lubricant may also be used at its interface with the hubstructure 52, such that a low friction surface is provided for the hubstructure 52 to contact should the pulley 26 move axially duringoperation, e.g., in the case of a pulley misalignment.

[0027] The pulley 26 is interconnected with the hub structure 52 by agenerally helical spring 118 mounted within the annular space 86. Thespring 118 is disposed in surrounding relation to the inner portion 96of the spring retainer 92, and is radially separated from the main coilsthereof by a clearance gap GI when no torque is applied thereto (i.e.,when at rest). While not shown, it can be appreciated by those skilledin the art that the spring 118 in the illustrated embodiment has one endbent axially outwardly, and this end extends within a notch formed inthe radial portion 57 of the hub structure 52 in order to fit one end ofspring 118 to the hub structure 52. The opposite end of the spring 118is bent to extend axially inwardly, and this end is engaged within anotch formed in the wall portion 104 of the spring retainer 92.Alternatively, a spring without a bent end could be engaged by pressfitting it into the radial portion 57 of the hub structure 52. Althougha spring 118 is shown in the illustrated embodiment which hasrectangular cross-sectioned volutes, a coil spring may also be usedwhich has circular cross-sectional volutes.

[0028] Disposed between the spring 118 and the pulley 26 and adjacentthe outer portion 100 of the spring retainer 92 is at least one springsleeve 105. The sleeve is preferably not a complete cylindricalconfiguration, but is split so as to provide a “C”-shaped configurationallowing it to expand and contract radially. If one spring sleeve 105 isused, it may extend the entire length between the outer portion 100 andthe end 61 of the axial portion 59 of the hub structure (a clearance gapis, of course, maintained between each end of the spring sleeve 105 andthe spring retainer and axial portion 59), thus covering a majority ofthe volutes of the spring 118. Alternatively, the at least one springsleeve 105 may include a plurality of spring sleeves 105 disposedadjacent to each other. The outer diameter surface 134 of the spring 118and the inner diameter surface 135 of the sleeve 105 is such that aclearance gap G2 is formed therebetween when no torque is applied to thespring (when the system is at rest). Alternatively, the clearance gap G2may exist between the spring sleeve 105 and the inner surface 86 of thepulley 26, depending on the particular fit of the spring sleeve 105around the spring 118. The spring sleeve 105 is preferably made of amaterial having a low coefficient of friction to facilitate slidingcontact of the spring 118 against the sleeve 105 when the spring expandsinto contact with sleeve 105. For example, the spring sleeve 105 ispreferably a nylon material. The material of the spring sleeve 105 mayalso a metal, such as brass, or a lead-alloy. In FIG. 2, a spring slipring 106 is also illustrated, disposed on a portion of the retainer 92proximate to the hub end of the spring 118. The spring slip ring 106 hasa “C”-shaped configuration similar to that of the spring sleeve 105 andperforms essentially the same function as the spring sleeve 105 in aradially spring-constricting direction, providing a low-frictionsliding-contact surface between the retainer 92 and the spring 118 whenthe spring 118 constricts against the retainer 92. The spring slip ring106 may be made of the same material as the spring sleeve 105, and mayor may not extend the entire length of the spring. Typically, if thespring slip ring 106 does not extend the full length of the spring 118,it is positioned proximate to the hub end of the spring, as the hub endis usually the first portion of the spring 118 to deflect under load.

[0029] The spring 118 may be installed within the annular space 86 in anaxially compressed state, between radially extending walls 57 and 104.In order to support the spring 118 in this state, a spring support 125is provided in the retainer 92, resting against retainer surface 104.The spring support is held in position by a tab that engages the samenotch in the retainer 92 that is used to secure the spring 118. Thespring support 125 is made of a low friction material such as nylon, andis contoured to follow the shape of the end surface of the installed,compressed spring 118. In general, the spring support 125 maintainsparallel coil alignment of the spring 118 once it is installed.

[0030] The wall 57 is axially fixed, as the hub is fixed to shaft 36.The wall 104 of the retainer 92 receives the axial load, which in turnis transmitted to pulley 26 as a result of the fixed connection betweenpulley 26 and retainer 92. Thus, the retainer 92 and pulley,26 arebiased towards the left in FIG. 2 under the force of spring 118. Thishas the effect of axially compressing the radial portion 128 of theannular bushing between pulley 26 (wall 71 thereof) and the hubstructure 52 (wall 57 thereof).

[0031] The presence of this axial load is used as a source of torsionaldamping of the isolator device, which moderates the pulley 26 and hubstructure 52 velocity differential caused by torsional inputs from theengine. The amount of torsional damping may be engineered by adjustingthe axial spring rate of spring 118. The torsional damping is enabled tosome degree as a result of the ability of the pulley to move slightlyaxially under the load of spring 118 through sliding engagement of theteflon coated surface of radial bushing 112 on hub sleeve 54. Thepress-fit insertion of spring retainer 92 against the surface portion 74of the pulley 26 is the last step in the assembly of coupling assembly29, and axially retains all components within the assembly 29.

[0032] The level of torsional damping is designed to increase withincreasing application of torque. That is, as a positive torque isapplied to the spring 118 as a result of the pulley 26 being driven bybelt 20, inner diameter 130 of the spring 118 decreases, resulting in anincrease in spring length. In other words, as the coils radially tightentowards the shaft axis as a result of the pulley 26 being driven, thecoils are also caused to expand axially. This increase in length, inturn, causes an increase in the axial load reacting against the radialportion 128 of bushing 78, thus damping in movement between pulley 26and hub 52. At the same time, as the torque increases, the diameter ofthe wire spring 118 decreases until the point where its inner diameter130 contacts the outer surface 98 of the inner portion 96.:of the springretainer 92, which causes a sharp increase in spring rate of spring 118.This significantly limits further deflection of the spring in theradially inward and axially outward directions. For example, and notintended to be limiting, the spring rate of spring 118 has been shown toincrease from about 0.4 Nm/deg prior to contacting the spring retainer92 to more than 3 Nm/deg after contacting the spring retainer 92. Theamount of radially inward deflection of the wire spring 118 can bevaried by engineering the clearance gap G1 between the inner diameter130 of the wire spring 18 and the spring retainer's 92 inner ring outerdiameter 98. Though not intended to be limiting, the system may beengineered such that between about 25-35 degrees, (in one preferredexample 30 degrees) of positive rotational movement of the pulley 26relative to hub 52 is established (relative to the at-rest position)before contact is made by the spring 118 with the inner portion 96 ofthe spring retainer 92.

[0033] It will be understood by those skilled in the art during mostdynamic operating conditions there are substantially very low loads onthe spring 118, and the spring is generally not in contact with theinner portion 96 of the spring retainer or the spring sleeve 105. Ingeneral, the spring 118 is caused to contact the inner portion 96 of thespring retainer only during abrupt system changes such as during enginestart-up. It is during such abrupt changes during start-up that thespring 118 would undergo the most torsional stress, for example in theaforementioned U.S. Pat. No. 5,139,463.

[0034] Of course, after this initial spring radial contraction, anopposite recoiling force will exist, as a result of the shaftacceleration momentarily exceeding that of the pulley, thus causingrelatively significant expansion of the spring 118, until the outerdiameter of the spring 118 contacts the inner surface 135 of springsleeve 105, again such contact having the result of increasing thespring rate.

[0035] The amount of expansion is controlled by the clearance gap G2between the outer diameter 134 of the spring 118 and the inner diameter135 of the spring sleeve 105. Preferably, this reverse travel (i.e.,negative, expansion direction) of the spring 118 is limited to be muchless than that of the forward direction (i.e., positive, contractiondirection) to reduce the stress in the spring 118 and improve componentdurability. For example, though not intended to be limiting, the springmay be sized such that 5-10 degrees of negative rotational movement ofthe pulley 26 relative to the hub 52 (with respect to the relativeangular positions when the system is at rest) is achieved beforesufficient spring expansion causes contact to be made with the springsleeve 105. In the absence of this travel control (both in the positiveand negative directions) the spring 118 could potentially be subject tolarge displacements which may result in fatigue of the spring.

[0036] Though not intended to be limiting, during an engine start-up,the spring may behave as follows. The wire spring 118 may contract andcontact the inner portion 96 of the spring retainer 92, and then expandto contact the spring sleeve 105. The wire spring 118 may repeat theabove motion at least once more before the applied torque in the springdiminishes and the spring 118 does not contact either the inner portion96 or the spring sleeve 105 to achieve steady dynamic state.

[0037] The axial load in the spring 118 applied to portion 128 ofbushing 78 also helps to slow the relative motion between the hubstructure 52 and the pulley before spring 118 contact is made in eitherdirection, which thus dissipates some energy as heat, rather thanabsorbing this energy in the spring 118.

[0038] Before the spring 118 deflection is limited in either directionby contacting the spring retainer 92 (in the positive direction) orspring sleeve 105 (in the negative direction), the clearance gaps G1 andG2 must first be taken-up by the spring. When the spring 118 contractsto contact the spring retainer 92, the spring 118 exhibits a significantincrease in its spring rate. Likewise, a significant increase in springrate is realized when the spring 118 expands so that the outer diameter134 of the spring 118 contacts the sleeve 105. In this manner, a spring“soft stop” is created, as opposed to a solid contact between the pulley26 and hub structure 52, when relative rotation therebetween reaches apredetermined level.

[0039] In the above embodiment, the pulley 26 is interconnected to thehub structure 52 by the coil spring 118, and spring retainer 92. Whenthere is a positive torque transmitted by the belt 20 to the pulley 26,the rotational movement of the pulley 26 will be imparted to the hubstructure 52 and, hence, the entire armature assembly 48 of thealternator, through the coil spring 118. During normal operation of theengine (i.e., after start-up), the resiliency of the coil spring 118enables the alternator armature assembly 48 under these circumstances tohave instantaneous rotational movements with respect to the pulley 26 soas to accommodate the high inertia characteristics of the alternatorarmature assembly 48. Similarly, where negative torques are imparted tothe pulley 26 by the belt 20, instantaneous relative motion of thealternator armature assembly 48 with respect to the pulley 26 isaccommodated so that any tendency for the belt 20 to slip with respectto the pulley 26 due to changes in torque in the belt 20 and the highinertia of the alternator armature assembly 48 are generallyaccommodated so as to minimize belt slippage.

[0040] For the purposes of this disclosure, the portion 96 of the springretainer 92 between the spring 118 and hub 54 may be termed as an innerspring engaging structure, while the sleeve 105 may be termed on outerspring engaging structure.

[0041] It will be understood that the characteristics of the spring 118are tuned to the particular drive system and more particularly to theparticular characteristic of the engine of the drive system. Thestrength of the spring 118 is determined by diameter dimension of thesteel utilized to form the coil. Proper tuning is determined by thespring rate which is a function of the number of turns or volutesincluded between the spring ends 121 and 123.

[0042] Although not shown in FIG. 2, it will be appreciated that a capmay be installed over the exposed end of the pulley 26 once the couplingassembly 29 has been installed to protect the internal components of thecoupling assembly 29 from contamination. The cap may, for example, becomprised of an injection-molded plastic material.

[0043] In an alternative embodiment, the spring 118 may be constructedsuch that each successive volute is decreasing in inner and outerdiameter 130, 134 (shown in FIG. 4). With this configuration, aspositive torque is applied to the spring, the spring 118 volutes contactthe outer diameter of the inner portion 96 of the spring retainer 92 insuccessive manner, which results in a progressive rising rate in springstiffness. Similarly, as negative torque is applied, the spring 118volutes contact the inner cylindrical surface of the spring sleeve 105in successive manner, causing a progressive rising rate in springstiffness.

[0044]FIG. 5. shows another embodiment of the decoupler, which isgenerally indicated as numeral 229. In this embodiment, the end 260 ofthe hub structure 252 radially extends for engagement with thecorresponding end 228 of the pulley 226. An annular, radial bushing 278may be disposed between the end 260 of the hub structure 252 and the end228 of the pulley for facilitating sliding contact therebetween. Theradial bushing 278 is of the same material as that described of bushing78 in the previous embodiment, and a lubricant may be applied thereto.The bushing 278 may include a protruding tab 281 for engagement with anindentation 273 formed in the contact surface 277 of the pulley 226 forfixing the axial position of the radial bushing 278. It can beappreciated that the protruding tab 281 may be formed on an oppositeside of the radial bushing 278 for engagement with an indentation (notshown) formed in the hub structure 252.

[0045] As seen in FIG. 5, the axial load of the spring 118 (which isinstalled as described above in the previous embodiment) is received bya thrust washer 229 on the opposite side of the spring 118, comparedwith the FIG. 2 embodiment] In this embodiment, a rigid spacer 266 andthe thrust washer 229 are disposed between the decoupler 229 and thealternator assembly 46. As will be understood by those skilled in theart, a portion of the axial load of the spring 118 is also taken up bythe hub structure 52 by the bearing contact of the pulley 226 via theradial bushing 278. An inner portion of the spacer 266 is axiallysqueezed between the hub 252 and the inner race of a ball bearingassembly 50 of the alternator assembly 46. The thrust washer 229 isdisposed between the back side of connecting wall portion 104 and aflange portion 267 of the rigid spacer 266. The thrust washer 229 may bemade of the same low coefficient of friction material as the annularbushing 78 of the previous embodiment, and the thrust washer supportsrelative motion between the shaft 36 and the pulley 226. Though thespring 118 in FIG. 5 is shown as having varying diameter coils, thediameter of the coils may be substantially the same, as with the firstembodiment. The interaction between the spring 118 and other componentsof the decoupler 229 is the same as that described in the firstembodiment.

[0046] Although the present discussion herein and throughout describesthe decoupler 29 as being mounted to an alternator, it will beunderstood by those skilled in the art that the decoupler of the presentinvention can be mounted on any other similar device.

[0047] While the invention has been described with reference to thecertain illustrated embodiments, the words which have been used hereinare words of description, rather than words or limitation. Changes maybe made, within the purview of the appended claims, without departingfrom the scope and spirit of the invention in its aspects. Although theinvention has been described herein with reference to particularstructures, acts, and materials, the invention is not to be limited tothe particulars disclosed, but rather extends to all equivalentstructures, acts, and materials, such as are within the scope of theappended claims.

What is claimed:
 1. A decoupler, comprising: a hub structure capable ofbeing mounted on a shaft; a pulley mounted on the hub structure andcapable of relative rotational movement with respect to said hubstructure; a coil spring resiliently coupling said pulley with said hubstructure, said coil spring capable of transmitting driven rotationalmovements of said pulley to said hub structure; an inner spring engagingstructure rotationally fixed with respect to said pulley and engagingvolutes of said coil spring as a result of radial contraction of saidcoil spring.
 2. A decoupler according to claim 1, further comprising anouter spring engaging structure disposed between said alternator pulleyand said coil spring, said outer spring engaging structure engagingvolutes of said coil spring as a result of radial expansion of said coilspring.
 3. A decoupler, comprising: a hub structure capable of beingmounted on a shaft; a pulley mounted on the hub structure and capable ofrelative rotational movement with respect to the hub structure; a coilspring resiliently coupling said pulley with said hub structure, saidcoil spring transmitting the driven rotational movements of said pulleyto said hub structure; an outer spring engaging structure disposedbetween said alternator pulley and said coil spring, said outer springengaging structure engaging volutes of said coil spring as a result ofradial expansion of said coil spring.
 4. A decoupler according to claim3, further comprising an inner spring engaging structure rotationallyfixed with respect to said alternator pulley and engaging volutes ofsaid coil spring as a result of radial contraction of said coil spring.5. A decoupler, comprising: a hub structure capable of being mounted ona shaft; a pulley mounted on the hub structure and capable of relativerotational movement with respect to the hub structure; a coil springresiliently coupling said pulley with said hub structure, said coilspring capable of transmitting driven rotational movements of saidpulley to said hub structure; said pulley being mounted for axialmovement relative to said hub structure; and said coil spring axiallyexpanding during radial contraction thereof and thereby applying anincreasing axial damping force on said pulley so as to dampen rotationalmovement of said pulley relative to said hub structure.
 6. A decoupleraccording to claim 5, further comprising a bearing between said hubstructure and said pulley, said bearing being increasingly axiallycompressed during said axial expansion of said coil spring.